Enhancement of permanent deformation resistance of modified asphalt concrete mixtures with nano-high density polyethylene

Abstract

The present research was carried out to inspect the influence of Nano-High Density Polyethylene (Nano-HDPE) particles and Styrene-Butadiene-Styrene (SBS) on the rheological characteristics of modified asphalt binders and performance of modified asphalt concrete mixtures. In this study, the base asphalt binder of the PG (64-16) grade was modified with Nano-HDPE and SBS polymers at a concentration of 3% and 5% by weight of total asphalt binder content. The Superpave dynamic shear rheometer (DSR), rolling thin film oven (RTFO), rotational viscosity (RV), pressure aging vessel (PAV) and bending beam rheometer (BBR) were conducted to evaluate performance grade of base and modified asphalt binders, also gyratory compactor was used to find optimum asphalt content. Roller compactor and wheel track tests were utilized to assess the rutting performance of modified asphalt mixture with Nano and SBS polymers, and the Indirect Tension Test (IDT) was used to assess the strength of mixtures before and after water conditioning. The results of the study show that Nano-HDPE particles have a considerable influence on improving Performance Grade (PG) of the binder, but at an equal concentration of polymer, it is not as effective as the SBS. However, the HDPE shows a significant advantage in keeping the viscosity of the modified binder at significantly lower levels and thus allowing much lower mixing and compaction temperatures as determined by the equ-viscous standard procedure. Although the PG grades of the binders showed the SBS to be more effective in improving the high-temperature grade than the HDPE, the mixture rutting performance shows that the HDPE modified binders provide better rutting resistance at 3% and 5% than the SBS modified binders. This finding shows that binder testing of G*/sin δ only could give a misleading indication of the true contribution of modified binders to rutting resistance as polymers could improve mixtures in different mechanisms than what is measure with binder PG testing. The IDT testing also shows that the strength of the mixtures produced with the modified binders at 25 °C is superior to the control mixture, with the HDPE providing slightly higher strength values before and after water conditioning. The overall results of the study show that HDPE can be used as a viable modifier requiring lower mixing and compaction temperature and equal or significantly better rutting and strength performance than conventional SBS Modifier. The study also highlights the need to check mixture performance when using specialty modifiers and not depend on only DSR testing as specified in the Superpave PG grading.